Method of chemically reacting substances in a reaction column

ABSTRACT

A process carried out in a reaction column for the chemical reaction of substances the reaction of which is affected by an unfavorable equilibrium position of the main reaction or a preceding equilibrium, wherein during the reaction one or more substances to be separated are continuously removed from the reaction mixture by one or more auxiliaries.

This application is a 371 of PCT/DE96/02056 filed Oct. 26, 1996.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a process carried out in a reactioncolumn for the chemical reaction of substances the reaction of which isaffected by an unfavorable equilibrium position of the main reaction ora preceding equilibrium, wherein during the reaction one or moresubstances to be separated are continuously removed from the reactionmixture by one or more auxiliaries.

2. Description of the Prior Art

In the past, reactive distillation proved successful in processeswherein conversion is impaired by the position of the chemicalequilibrium forming the basis for reaction. Besides the production ofethers which are used for example as antiknock additives in fuels,esterification is another field of application. Prior art processes ofesterification are reactive distillation processes allowing continuousseparation of the water from reaction by distillation. See e.g. J.Krafczyk and J. Gmehling, Chem. Ing. Tech., vol. 66 (1994), p. 1372; andC. Breucker, V. Jordan, M. Nitsche, and B. Gutsche, Chem. Ing. Tech.,vol. 67 (1995), p. 430. During conventional reactive distillation thetemperatures in the column are such that all substances, except for thebottoms, are heated to boiling point.

In the known processes, separation of the water from reaction iseffected by a reactant which, in most cases, must be charged in highexcess. It is therefore necessary that at the given pressure thetemperature for separation be equal to or higher than the distillationtemperatures of the reactants. The reactants employed in said processesare an auxiliary and an additional substance. In esterificationprocesses the alcohol, if used in excess, is both the reactant for theesterification reaction and the auxiliary for removing the water fromreaction. Furthermore, it is necessary to determine the ratio at whichthe reactants are used in order to achieve efficient separation.According to C. Breucker et al., separation of the water from reaction,if the reactants are present in low excess, is a challenging task forprocess engineers. Up to now, this problem has been tackled by usingbatch or cascade processes employing several reactors.

One embodiment which is well known in the art is the one-stageesterification using an entraining agent and taking advantage ofazeotrope formation. See e.g. Organikum, VEB Deutscher Verlag derWissenschaften, Berlin (1977), p. 71-73. Processes for producing estersfrom carboxylic acids and alcohols with continuous separation ofcondensed water in a column using entraining agents, such as benzene,methanol, and butyl alcohol are described in DE 976 413 B. Theentraining agent used according to U.S. Pat. No. 2,384,793 is butane.

WO 94/19079 discloses a process for producing bisphenol A from acetoneand phenol while splitting off water. The resultant water from thereaction is removed using an inert stripping gas. The aforesaid processemploys a reactor containing a liquid catalyst or a particulate,suspended catalyst, while the reactor itself is equipped with trays,drains, and/or hold-back screens.

BRIEF SUMMARY OF THE INVENTION

It is the object of the present invention to provide a process allowingto enhance the conversion in equilibrium reactions and, in particular,to remove a substance which has formed and must be separated in acontinuous, gentle, and most effective way in a column by using anauxiliary.

It was surprisingly found that in columns with fixed-bed catalystspermanent gases are particularly suitable stripping gases serving thisend. The advantageous effect of the stripping process should be utilizedto support the reaction course and to prevent at the same time that areactant is present in high stoichiometric excess. Once the auxiliaryhas fulfilled its task, it should be returnable to the process in asimple way. By using the present process it should be possible to avoidcoupling of the process parameters, such as processtemperature-pressure-distillation temperature-educts ratio, which isinherent to prior art processes.

According to the present invention, the problem is solved by a processcarried out in a reaction column for the chemical reaction of substancesthe reaction of which is affected by an unfavorable equilibrium positionof the main reaction or a preceding equilibrium, wherein during thereaction one or more substances to be separated are continuously removedfrom the reaction mixture by one or more auxiliaries. This is achievedby passing a stripping gas, i.e. a permanent gas or a mixture ofpermanent gases, as an auxiliary through the reaction column in which asolid catalyst is arranged as a fixed bed and adjusting temperature andpressure such that all the educts are present as liquids or as solutionsof solids and that the substance(s) in the reaction column is (are)predominantly present in gaseous/vaporous form. The stripping gas ispreferably led countercurrently to the liquid stream. Stripping andreaction take place simultaneously in the reaction column. The catalystmay be arranged as a regular packing or an irregular bulk.

DETAILED DESCRIPTION OF THE INVENTION

The continuously charged auxiliary is a permanent gas. According to thepresent invention, permanent gases are gases which cannot be liquefiedat temperatures of greater than -30° C. Furthermore, permanent gases asdefined in the present invention are gases consisting of 5 or feweratomic molecules and mixtures thereof, including C₁ hydrocarbons.Particularly suitable substances are those the molecules of whichconsist of only one element, such as nitrogen (N₂) or hydrogen (H₂),hydrogen being particularly preferred. Said permanent gases serve asstripping gas for the product to be separated. This stripping gasdiffers from a conventional entraining agent in that it is alreadypresent in gaseous form, whereas the entraining agent must first beconverted to a gas.

Considerable evaporation heat is required for this conversion. Moreover,it is essential that the product to be withdrawn from the equilibrium bealso present in the gaseous phase. In the instant case it can partly bepresent as a liquid.

The process according to this invention is of advantage whenever it isimpossible to heat all the reactants or products to boiling point whichwould result in decomposition of the products or undesired sidereactions. In said cases, prior art reactive distillation processescannot be employed because the reactants would decompose. Therefore, theinstant novel process is particularly suitable whenever natural ortemperature-sensitive substances are to be converted. During thisconversion the continuous removal of a low-molecular reaction producthas a favorable effect on the course of reactions wherein the reactantsmust not be heated to boiling point.

The catalyst is a fixed-bed catalyst. In a preferred embodiment thereaction column is operated as a trickle column of which about 30 to 60vol %, preferably 50 vol % are utilized by the stripping gas as free gasspace, whereas 30 to 50 vol %, preferably 40 vol % of the column isoccupied by solid substance, i.e. the fixed-bed catalyst. The remainingreaction space, preferably 10 vol % or less, is occupied by thetrickling liquid. Irrespective of other process parameters, highcatalyst concentrations can be chosen in a wide range. In contrast toprior art processes, the ratio of catalyst:liquid phase is surprisinglyhigh.

When using a fixed bed, the residence time of the liquid phase can beadjusted by the stripping gas velocity. The residence time of the liquidphase is high with higher velocities of the stripping gas volume. Thestripping gas throughput can be adjusted in a wide range without havingan adverse effect on the course of process.

The effect of the stripping gas can be modified by an additionalauxiliary which is a conventional entraining agent, such as benzene,toluene, or hexane, the latter one being particularly preferred. In thiscase the stripping gas removes the substance to be separated togetherwith the entraining agent which is in gaseous form under the operatingconditions in the stripping column.

When using entraining agents as auxiliaries in addition to permanentgases, the amount of permanent gas in the reaction column is greaterthan 80 mol % of the auxiliaries charge, while the amount of entrainingagent accordingly makes up to 100 mol %. The molecular portion ofentraining agent is by at least the factor 4 smaller than the amount ofpermanent gases in the reaction column.

Reactions for which this novel process can be employed generally proceedaccording to the following equation: ##STR1##

At least one of the products--the substance to be separated--can bevaporized under the reaction conditions of the reaction stripper or canbe converted to vapor by the stripping gas. The reaction is anequilibrium reaction or is influenced in its course by a precedingequilibrium. The following types of reaction are given as examples:

Aldol Condensation ##STR2## Knoevenagel Condensation

This condensation is a special case of aldol reaction followed by aldolcondensation: methylene components having particularly high CH acidity,such as malonic acid, malonic semi-ester, malonic ester, cyanoaceticacid, cyanoacetic acid ester etc., are reacted with aldehydes andketones. ##STR3## Example of a Substance

The reactants are sensitive to temperature and have higher boilingpoints than the auxiliary. The water to be separated (substance to beseparated) is removed by the stripping gas, or the water to be separatedplus an additional entraining agent, such as hexane, benzene, ortoluene, hexane being the preferred entrainer, form an azeotrope inwhich case the permanent gas leaves the reaction stripper overheadtogether with entraining agent and water. The product, benzal malonicacid diethyl ester, is the highest boiling substance (186° C. at 18torr) leaving the column at the bottom.

    ______________________________________                                        Reactants                                                                              Boiling Point                                                                           Catalyst        Auxiliary                                  ______________________________________                                        Benzaldehyde                                                                           177° C.                                                                          Bases, e. g. basic ion ex-                                                                    Stripping gas                                  changers, carbonates of or stripping                                          alkali metals and alkaline gas + hexane                                       earth metals                                                                Malonic acid 94-96° C.                                                 diethyl ester at 11 torr                                                    ______________________________________                                    

Preparation of Enamines

Enamines are formed by reaction of aldehydes and ketones with secondaryamines. This route is an important one for the formation ofintermediates for organic syntheses. An important field of applicationis the formation of heterocycles employing appropriate reactants.##STR4## Example of a Substance

Like in the example given hereinabove, the product β-benzylaminocrotonic acid ethyl ester is the highest boiling substance (b.p.140° C. at 0.5 torr). The stripping gas or stripping gas plus entrainingagent as an auxiliary transport the water (substance to be separated) tothe top of the apparatus. The product leaves the reaction stripper atthe bottom.

    ______________________________________                                        Reactants                                                                              Boiling Point                                                                           Catalyst        Auxiliary                                  ______________________________________                                        Acetoacetic                                                                            68-79° C.                                                                        Acids, e. g. acidic ion ex-                                                                   Stripping gas                                acid ethyl at 11 torr changers or toluene sul- or stripping                   ester  fonic acid gas + hexane                                                Benzyl amine 70-71° C.                                                  at 10 torr                                                                 ______________________________________                                    

Reactions of Carbonyl Compounds with Bases

Reactions of carboxylic acids with amines to form carboxylic acid amides

Formation of the acid amide is favored by the continuous removal ofwater (substance to be separated) in the reaction stripper. Thewater-enriched auxiliary leaves the apparatus overhead, whereas theproduct is withdrawn at the bottom. ##STR5## Example of a Substance

    ______________________________________                                        Reactants                                                                              Boiling Point                                                                           Catalyst        Auxiliary                                  ______________________________________                                        Capronic acid                                                                          205° C.                                                                          Acids, e. g. acidic ion ex-                                                                   Stripping gas                                  changer or stripping                                                           gas + hexane                                                               Dibutyl amine 159-161° C.                                            ______________________________________                                    

Guerbet Reaction ##STR6## Esterification of Carboxylic Acids ##STR7##Example of a Substance

    ______________________________________                                        Reactants  Catalyst    Auxiliary                                              ______________________________________                                        Isobutanoic acid or                                                                      Acids, e. g. acidic                                                                       Hydrogen as a stripping gas,                             pivalic acid with hy- ion exchanger optionally together with                  droxybenzaldehyde  benzene, toluene, or, preferably,                            hexane                                                                    ______________________________________                                    

Reactions of fatty acids with fatty alcohols to form fatty acid esters

It is an advantage of the process according to this invention that whenusing permanent gases as an auxiliary, ordinary coolers can be mountedinto the condensers because the physical data of the permanent gaseseffecting the separation of substance are often very different fromthose of the substances to be separated (boiling point, heat ofcondensation, heat of evaporation). Thus, less energy is required forpreheating because heat is only required for raising the temperature ofthe gas to reaction temperature, but not for heating a liquid entrainingagent to effect vaporization. ##STR8## Example of a Substance

    ______________________________________                                        Reactants      Catalyst  Auxiliary                                            ______________________________________                                        Fatty acid     Acids, e. g.                                                                            Hydrogen or nitrogen as a                              C.sub.6 --C.sub.22, preferably C.sub.8 --C.sub.22 acidic ion stripping                               gas, optionally                                        Fatty alcohols exchanger together with hexane                                 C.sub.1 --C.sub.22, preferably C.sub.8 --C.sub.22  (azeotrope former)       ______________________________________                                    

Advantageous embodiment of this process

(general, applicable to any reaction variant)

BRIEF DESCRIPTION OF THE DRAWING

A particularly advantageous embodiment of this process is shown inFIG. 1. A mixture of reactants is charged to the upper section of thereaction stripper. Chemical reaction takes place while the liquidreaction mixture, as a result of gravity, flows down via the stripperpacking. The packing can be made of a solid or supported catalyst. Alsosuitable is an at least partially inert packing. The product obtainedwhich is to be separated evaporates and is removed from the reactionzone by a stream of an auxiliary which is preferably chargedcountercurrently from the bottom. The auxiliary enriched with thesubstance to be separated leaves the reaction stripper overhead. Aftercondensation of the substance to be separated, the auxiliary can bereturned to the apparatus or, as a reactant, to a subsequent processstage. The desired liquid reaction product leaves the reaction stripperat the bottom.

When separating the water from reaction by means of an auxiliary, thereaction can be influenced to the advantage of the desired product, e.g.fatty acid ester. As shown in FIG. 1, a mixture consisting e.g. of fattyacid and fatty alcohol is charged to the upper section of the reactionstripper. Alternatively, the educts can partially be reacted by apreceding reaction which has the advantage of achieving the sameconversion in a shorter reaction stripper column. In this case theproduct from the preceding reaction is charged to the reaction stripper.

Temperature and pressure of the reaction stripper are such that both thetwo reactants and the product, e.g. fatty acid ester, are liquid, whilethe component to be separated, e.g. water, evaporates and is mainlypresent in vaporous form.

The stripping gas, e.g. preheated, dry hydrogen, charged to the bottomof the apparatus flows to the top of the reaction stripper. Whilepassing through the apparatus, it entrains the component to beseparated, e.g. water. The hydrogen enriched with the component to beseparated, e.g. water, leaves the apparatus overhead and reaches acondenser wherein it is separated from the component to be separated,e.g. water. Optionally, the hydrogen can be returned to the reactionstripper or may be employed in a different way. It is also possible tocharge one of the reactants, preferably the alcohol, through a lateralinlet into the reaction stripper. This variant raises a furtherpossibility of influencing the reaction to the advantage of theproducts. Furthermore, this process variant allows to control thetemperature profile in the reaction stripper by preheating the sidestreams. It is a particular feature of the process according to thisinvention that the educts, e.g. carboxylic acid or, in the case oftransesterification, the carboxylic acid ester, and the alcohol canadvantageously be employed in equimolar quantities. If, however,overstoichiometric conversion is desired, the alcohol is charged inexcess quantity. The product, e.g. the fatty acid ester, is removed fromthe lower section of the column.

The reaction stripper is provided with a solid catalyst. Thus, thereaction rate which is already accelerated by the stripping procedurecan be further increased. When employing acidic catalysts, e.g. for anesterification process, it is expedient to use a solid acid as catalyst,e.g. an acidic ion exchanger. Ion exchangers which can also be employedat high reaction temperatures of up to 230° C. are particularlysuitable. Water-sensitive catalysts, e.g. catalysts which adsorb thewater from reaction, can be reactivated by drying after several cyclesin order to increase conversion.

The process temperature is from 20 to 300° C., preferably 100 to 230° C.The process pressure is below atmospheric down to 50 bar, preferably 1.5to 15 bar. It is surprising that during esterification a cross-sectionalload of the liquid phase of <0.48 kg/m² s has no perceptible effect onthe fatty acid conversion, whereas at >0.48 kg/m² s the conversiondecreases, as is expected, as the cross-sectional load increases.

It is understood that any other reaction meeting the requirementsdescribed hereinabove can advantageously be carried out according to thenovel process described herein. This process can be employed wheneverthe educts or products are higher-boiling, temperature-sensitivesubstances, e.g. in the production of intermediates for detergents,pharmaceuticals, and cosmetics. The reactions mentioned herein are onlyfew examples of a large number of syntheses which can be performedemploying the novel process presented herein.

Examples of Experiments

Experiments were carried out in a batch reactor in order to examine thekinetics of fatty acid esterification under stripping conditions.Furthermore, experiments were carried out in a lab-scale reactionstripper.

Batch Reactor Experiments

Fatty acid and fatty alcohol were charged to a batch reactor. Theesterification reaction was carried out in the presence of a suitablecatalyst. The acidic catalyst (ion exchanger) having the form of Raschigrings was arranged as a fixed bed in the reactor. The reaction volume ofabout 400 ml was filled with about 85 ml of solid catalyst. The liquidphase volume was about 230 ml. The remaining volume was the strippinggas volume. Nitrogen was employed as a stripping gas. This batch reactorsimulates a section in a reaction stripper column.

The volume ratios of catalyst:liquid phase:gaseous phase chosen hereinare not applicabe to a reaction stripper column. Despite the unfavorableparameter, i.e. the relatively low catalyst concentration in proportionto the liquid phase, the experiments proved that the process of thisinvention offers some advantages. Reaction temperature, feed ratio ofthe reactants, and volume of the stripping gas stream were varied inthese experiments.

    ______________________________________                                                  Fatty Acid Conversion [-] at                                          Equimolar Feed Ratios                                                                              120 I N.sub.2 /h (Volume of Stripping                    Reaction Time [min] 0; 17; 60 I N.sub.2 /h Gas Stream)                      ______________________________________                                        20          ≈0.2                                                                             0.5                                                      40 ≈0.4 0.7                                                           75  ≈0.62 0.8                                                       ______________________________________                                    

It became apparent that the conversion of ester increases significantlywith the reaction time if at the same time stripping gas is led throughthe batch reactor. This is achieved by the improved removal of theby-product water according to this invention by means of the strippinggas stream. The conversion increases as the stripping gas streamincreases with time. The effect of simultaneous stripping in a batchreactor is not felt when employing very small stripping gas streams (<60liters of nitrogen per hour). The experiments carried out in a batchreactor revealed that at a reaction temperature of 110° C. andatmospheric pressure the stripping gas stream (in this case nitrogen)should be greater than about 0.025 kg of nitrogen/(m² s). The referencearea is the cross-sectional area of the empty reaction stripper. Theexperiments were carried out in such a manner that the by-product to beeliminated, water, is obtained at a point above its boiling point. Fromprocess engineering aspects, this is the more advantageous variant ofevaporation stripping.

In the second series of experiments the reaction temperature was 80° C.at atmospheric pressure. In these experiments water was obtained belowits boiling point, i.e. as a liquid. In this case, too, it could beproved that the conversion increases by simultaneous stripping. However,the stripping efficiency was lower.

    ______________________________________                                                      Fatty Acid Conversion [-]                                          at Equimolar Feed Ratios 129 I N.sub.2 /h                                    Reaction Time [min] (Volume of Stripping Gas Stream)                        ______________________________________                                        20            0.07                                                              40 0.13                                                                       75 0.25                                                                     ______________________________________                                    

Experiments in a Lab-Scale Reaction Stripper

A lab-scale reaction stripper was developed in order to prove thefeasibility of the stripping process according to this invention in acolumn. The column had an internal diameter of 80 mm. For the firstexperiments a fixed catalyst bed consisting of acidic ion exchangers inthe shape of Raschig rings was employed. The catalyst bed had a lengthof 1 m. The volume of the catalytic Raschig rings packing was about 5liters. Equimolar quantities of fatty acid and fatty alcohol werecharged to the top of the apparatus, while the stripping gas was fedcounter-currently from the bottom. In the first experiments nitrogen wasemployed as a stripping gas.

    ______________________________________                                        Cross-sectional load with liquid phase                                                              0.24    kg/(m.sup.2 s)                                    (fatty acid + alcohol)                                                        1.sup.st  cross-sectional load with nitrogen stripping 0.049 kg/(m.sup.2                                   s)                                               gas                                                                           2.sup.nd  cross-sectional load with nitrogen stripping 0.085 kg/(m.sup.2                                   s)                                               gas                                                                           3.sup.rd  cross-sectional load with stripping gas 0 kg/(m.sup.2 s)                                         Reaction temperature 110° C.                                           Reaction pressure  atmospheric                 ______________________________________                                    

Conversion of the fatty acid increased as the stripping gas streamincreased (at least with small-volume to medium-volume streams).

Conversion [-] as a function of the volume of stripping gas stream aftera reaction time of 90 minutes at V_(I),ges ≈5.1 I/h, T=110° C., andatmospheric pressure

    ______________________________________                                        0          NI N.sub.2 /h  (3)   0.15                                            1,500-2,000 NI N.sub.2 /h (2) 0.27                                          ______________________________________                                    

It was also found that the water content in the products decreased asthe stripping gas stream increased (at least with low-volume tomedium-volume streams), i.e. the quality improved.

Water content after a reaction time of 85 minutes at V_(I),ges 26 5.1I/h, T=110° C., and atmospheric pressure

    ______________________________________                                        0.25 wt. % H.sub.2 O                                                                         at 1,500-2,000 NI N.sub.2 /h                                                                 (2)                                               0.39 wt. % H.sub.2 O at 0 NI N.sub.2 /h (3)                                 ______________________________________                                    

Further experiments were carried out employing hydrogen as a strippinggas. The start-up behavior of the lab-scale reaction stripper wasexamined at two pressures. The pressures were chosen such that at a lowpressure the water was obtained as a gas, while at a high pressure thewater was obtained as a liquid. The other process parameters were:

    ______________________________________                                        Cross-sectional load with liquid                                                               0.48-0.54 kg/(m.sup.2 s)                                       phase (= fatty acid + alcohol)                                                1.sup.st  cross-sectional load with H.sub.2 3.15 · 10.sup.-3                                  kg/(m.sup.2 s)                                       stripping gas at 2 bar                                                        2.sup.nd  cross-sectional load with H.sub.2 1.42 · 10.sup.-3                                  kg/(m.sup.2 s)                                       stripping gas at 0.35 bar                                                     Reaction temperature 110° C.                                           1.sup.st  reaction pressure 2 bar above atmospheric                           2.sup.nd  reaction pressure 0.35 bar above atmospheric                      ______________________________________                                    

Like in the batch reactor experiments it became apparent that thestripping efficiency achieved by this evaporation stripping variant ishigher than in a process wherein the water is obtained as a liquid.

Conversion [-] as a function of the volume of stripping gas stream aftera reaction time of 90 minutes at V_(I),ges ≈10-11 I/h and T=110° C.

    ______________________________________                                        300  NI H.sub.2 /h at ≈2 bar pressure above atmospheric                                             (1)    0.082                                      300 NI H.sub.2 /h at ≈0.35 bar pressure above atmospheric (2)                                            0.118                                    ______________________________________                                    

Furthermore, the residence time of liquid phase and liquid phase hold-upas a function of the volume of liquid phase stream was examined. Whenthe liquid load in the reaction stripper was low, the hold-up was foundto decrease, while the residence time increased. With low liquid loadsthe residence time of the liquid phase could be influenced significantlyby the volume of the stripping gas stream. The reaction stripper ransmoothly even with wide variations of the liquid load (about 1:300 inthe experiments). The volume of the stripping gas stream, too, could bevaried in a very wide range, i.e. from 0 to about 1,000 l/h, withoutresulting in process stand- still for hydrodynamic reasons.

Further experiments for the esterification of fatty acids and fattyalcohols using an acidic ion exchanger (Amber-list) and hydrogen as astripping gas were carried out in a pilot plant. The fatty alcohol wasused in 10% excess. In order to determine the maximum conversion,several runs were performed at constant reaction parameters, theesterification product being returned to the process.

                  TABLE 1                                                         ______________________________________                                        Conversion per Run                                                                         Conversion [%]                                                   Experiment No.                                                                             (1)         (2)    (3)                                           ______________________________________                                        1            53.6        62.3   62.3                                            2 76   87   81.9                                                              3 89.8 90.6 89.6                                                              4 94.4 90.9 92.8                                                              5 96.6  93.3                                                                ______________________________________                                    

                  TABLE 2                                                         ______________________________________                                        Parameters (Volume of Stripping Gas Stream: 900 I H.sub.2 /h)                   Experiment No.                                                                              Pressure (above atmospheric)                                                                   Temperature                                  ______________________________________                                        1           0.35 bar         140° C.                                     2  0.5 bar 160° C.                                                     3   3 bar 180° C.                                                    ______________________________________                                    

What is claimed is:
 1. A process carried out in a reaction column forthe chemical reaction of substances, the reaction of which is affectedby an unfavorable equilibrium position of the main reaction or apreceding equilibrium, wherein during the reaction one or moresubstances to be separated are continuously removed from the reactionmixture by one or more auxiliaries, characterized in that:said chemicalreaction of substances comprises a condensation reaction to produce acondensation product wherein through the reaction column a solidcatalyst is arranged as a fixed bed; a stripping gas which is apermanent gas or a mixture of permanent gases is led as an auxiliary;and temperature and pressure are adjusted such that in the reactioncolumn all the educts are present as liquids or solutions of solids andthe substance(s) to be separated is (are) predominantlygaseous/vaporous.
 2. A process according to claim 1, characterized inthat hydrogen is employed as a stripping gas.
 3. A process according toany one of the preceding claims, characterized in that an entrainingagent is additionally used in order to remove the substance to beseparated.
 4. A process according to claim 1, characterized in that thesubstance to be separated is additionally removed by employing ahydrocarbon as an entraining agent.
 5. A process according to claim 1,characterized in that said condensation product to be separated has amolecular mass of less than 100 g/mole.
 6. A process according to claim5, characterized in that carboxylic acids are esterified with alcoholsto form carboxylic acid esters.
 7. A process according to claim 5,characterized in that carboxylic acid esters are transesterified withalcohols to form carboxylic acid esters.
 8. A process according to claim6, characterized in that C₆ -C₂₂ carboxylic acids are esterified with C₁to C₂₂ alcohols to form carboxylic acid esters.
 9. A process accordingto claim 7, characterized in that carboxylic acid esters having a C₆-C₂₂ acid group and a C₁ to C₄ alcohol group are transesterified with C₆to C₂₂ alcohols to form carboxylic acid esters.
 10. A process accordingto claim 1, characterized in that an acidic solid catalyst is employedin the reaction column.
 11. A process according to claim 1,characterized in that double bonds are simultaneously hydrogenated inthe reaction column by using hydrogen as a permanent gas and catalystsknown in the art.
 12. A process according to claim 1, characterized inthat a multifunctional catalyst is employed in the reaction column. 13.A process according to claim 1, characterized in that the stripping gas,optionally jointly with the entraining agent, is (are) contercurrentlyled through the reaction column from the bottom to the top, thesubstance to be separated is removed from the stripping gas and,optionally, the entraining agent in a condenser, and the stripping gasand, optionally, the entraining agent, or part thereof is (are) returnedto the reaction column.
 14. A process according to claim 1,characterized in that C₈ -C₂₂ acids are esterified with C₈ to C₂₂alcohols to form carboxylic acid esters.
 15. A process according toclaim 1, characterized in that carboxylic acid esters having a C₈ -C₂₂acid group and a C₁ -C₄ alcohol group are transesterified with C₈ to C₂₂alcohols to form carboxylic acid esters.
 16. A process according toclaim 12, characterized in that said multifunctional catalyst is of atype that can support an esterification reaction, a hydrogenationreaction, and/or an isomerization reaction.